Mandrel for tube rolling mills



Aug. 18, 1931.` P. MuLTHAuPT' 1,319,257

IIANDREL FOR TUBE ROLLING HILLS Filed Aug, 1o. 1929 Ffg.2.

Y /n vento/n' /M awr f5 Patented Aug. 18, 1931 UNITED sTATEs PAUL MULTHAUPT, OF DUSSELDORF, GERMANY MANDREL FOR TUBE ROLLING MILLS Application leyd August 10, 1929, Serial No. 384,916, and in Germany November 26, 1928.

In the production of tubes by rolling, first of all, in the skew rolling mills, the hot ingot-s are perforated 'with the help of mandrels, whereon the perforated ingots are then rolled out in the profile rolling mills to seamlesstubes likewise with the assistance of mandrels. These mandrels consist of a conicalshaped head, the profile of which at the edge of its base, determines the profile of the rolled tube, and `a shank carrying the said head, which shank is attached in the centre on the base of the head. Hitherto the head of the mandrel has been made of highly alloyed special steel or of hard cast iron; in spite of this, these mandrel heads last only a very short time and moreover they allow only comparatively short tubes to be made, since they are subjected not only to lhigh pressures but also to high temperature, so that they wear 20 out with extraordinary rapidity, particularly at their rear sealing edges projecting over the mandrel rod, which is decisive for the profile of the tube. The invention removes these disadvantages by this, that these mandrel heads or plugs are made of a particular material which does not come into the category of steels, and further that they are given a new shape, so that they are suiiciently resistant to render 3 possible the production .in considerable quantities of long tubes by rolling.

According to the invention the mandrels or the mandrel heads are made of tungsten or an alloy containing mostly tungsten. The extraordinary hardness of tungsten carbides is already known; also, it has already been proposed to utilizethis property for drawing matrices,rfor drilling, cutting, turning 40 and similar cold-working tools, by pressing into the desired shape the tungsten or tungsten carbide mixed or alloyed with other substances, after which the .shaped articles produced were subjected to a certain heating (up to 1500-1600 C.).

In the present case, however, hot-working tools are under consideration, which have to withstand not only a high temperature but, at the sameH time, a4 considerable pressure on all sides. Y

It has been found in a surprising manner that tungsten and alloys containing mostly tungsten possess at high temperatures an excellent resistance capability towards deforming forces and a great resistance towards fracture. The present invention depends tungsten-carbon alloys are extraordinarily hard, which is to be attributed to the tungsten carbides formed by the alloying, is also utilized. Thus, the mandrel heads made according to the invention last for a period which would be almost unlimited were it not that the ingots and tubes pushed over the heads of the mandrels gradually change the prole by grinding action; however the number of tubes which may be rolled down in rapid sequence on one mandrel head is. at least 50 times greater than is today possible with the best-known plug materlal.

The new mandrels may be made by melting and' casting, or, also by sintering. Thus, for example, the material consisting chiefly of tungsten is melted in a particular furnace, the highest attainable temperature being employed, and it flows after complete retining into the mould which is in the furnace, where it solidifies. The moulded article pro` duced in this manner, on account of its great hardness, can be ground to the size suitable for use only by means of diamond dust. Subsequent treatment by forging or jumping is not possible.

The `mandrels now in use, forged from steel, or cast from hard cast ironshow.at their strongest ends edges which are partly sharp and partly rounded, as is rendered necessary by the manufacturing process or other considerations. Because of the employment in bthe destruction of the cross-section of the l tu e.

The shape of the mandrel head shown in Figs. l and 2'of the accompanying drawings shall satisfy these conditions.

According to Fig. l, the mandrel head a seen in front shows the generally usual conical shape down to the sealing edge b which determines the profile, which edge is rounded 0E and passes into a fiat conical frustum c, to which is attached a plug d made of the same material as the head, and extending into the mandrel shank'e carrying the head.

The modification form shown in Fig. 2 is the same as Fig. 1 with regard to the shape of the head; but, in order to economize in tungsten, a cavity f is "provided in the mandrel head a on the rear side, which serves for the accommodation of a plu made, for example,

of iron; this plug pro]ects suiiiciently far from the mandrel head in order to be pressed in by means of this free end into a corresponding cavity g in the mandrel shank so as' to unite the head a centrally with the shank e.

The connecting plug may, if necessary, also be made in one piece with the mandrel rod, as then in general the union between the mandrel head and the shank may Ybe effected in any other desired manner.

The mandrel head a accordingly lies with the surface of the conical'frustum c on the shank e suitably turned out, which embraces 1t as 1t were 1n a suction-like manner 1n order to produce a uniform distribution of the pressure, whilst the head rounded off in the front part at the place of its greatest diameter projects only a little over the mandrel -shankelnasmallround portion (at 1)),whereby the conical part becomes the seat of pressure within the mandrel shank. This conical frustum c contributes to the production of a cast article free from stress and cavities since it forms a transition from the greatest mandrel diameter to the cast-onplug d, according to Fig. 1.

What I claim is v 1. A mandrel for-tube-rolling'mills comprisng in combination with the shank, a

ead made of tungsten.

2. A mandrel for tube-rollin mills comprisingin combination with t e shank, a head made of an alloy including a major amount of tungsten.

3. A mandrel for tube-rolling mills prising a head anda shank, said head includlng a rearwardly extending frustro-conical formation the base of which is of substantially the same diameter as the greatest diameter of the'head, the' shank having a frustro-conical end cavity, the base of whlch is of substantially -the same diameter as the base of the frustro-conical formation of the head and exactly fitting said formation, whereby the edge portions of the part of the'head of greatest diameter are supported by the shank against fracture.

4. A mandrel as set forth in claim 3 in which the shank is provided with a central recess opening into the frustro-conical cavity thereof, and a rearwardly extending lplug is provided on the frustro-conical formation of the head extending into said recess.

5. A mandrel as set for-th in claim 3 in which the head is provided with a central recess opening through the rear end thereof, and a plug extends forwardly from the shank into said recess. l

6. A mandrel as set forth in claim 3 in which the shank is provided with a central recess opening into the frustro-concal cavity thereof, and the head, is provided with a central recess opening through4 the rear end thereof, and a connecting plug extends into Y both of said recesses.

In testimony whereof I have signed myv sol 

